Starting and operating circuits for fluorescent lamps



Jan. 3, 1956 w, s, HAMlLTON 2,729,769

STARTING AND OPERATING CIRCUITS FOR FLUORESCENT LAMPS 2 Sheets-Sheet 1Original Filed June 6,' 1951 INVENTOR! )Vi/b'am 5. A. Ham/Won ATTORNEY.

1956 w. s. H. HAMILTON 2,729,769

STARTING AND OPERATING CIRCUITS FOR FLUORESCENT LAMPS Original FiledJune 6, 1951 2 Sheets-Sheet 2 WM/[am J. H Ham/W017, 431" ATTORNEY UnitedStates Patent "cc .,,,,,,f,;??;122

STARTING AND OPERATING CIRCUITS FOR FLUORESCENT LAMPS William S. H.Hamilton, Larchmont, N. Y.

Original application June 6, 1951, Serial No. 230,185. Divided and thisapplication February 18, 1953, Serial No. 337,487

4 Claims. (Cl. 315-100) This application is a division of my priorapplication Serial No. 230,185, filed June 6, 1951.

This invention relates to starting and operating circults forfluorescent lamps, and particularly for alternating current and directcurrent fluorescent lamps which are more or less diflicult to start andrequire an inductive kick to start them.

The primary object of the present invention is to provide in a startingcircuit wherein the preheating circuit is interrupted with unusualrapidity so as to provide an extremely high voltage impulse for startingthe lamp, a cut-out or lock-out mechanism which is reliable andeffective, to prevent further operation of the starting mechanism incase the lamp fails to start after a reasonable number of firingattempts have been made.

A further object of my invention is to provide a starting and cut-outsystem having a rapid response in restarting a lamp which has beenswitched out of operation.

Another object of the invention is to provide a starting and cut-outcircuit which can be embodied in the usual starter container and whichcan be reversed in its socket.

A still further object of the invention is to provide a starting andcut-out system which will effectively start lamps at low temperatures,such for example as 0 F. and below.

In the accompanying drawings, forming part of this specification,

Figs. 1, 2 and 3 are diagrammatic views of diflereht forms of circuitsfor D. C. or A. 0-D. C. use and which employ a starter embodying thequick restarter and the lock out means of the character described.

Fig. 4 is a diagrammatic view of a circuit similar to that of Fig. 3 butadapted solely for A. C. use.

Fig. 5 is a diagrammatic view of another circuit for use on A. C., inwhich special provision for starting, at cold temperatures, such as 0 F.and below, is provided.

Figs. 6, 7 and 8 are schematic obverse, reverse and side elevationalviews of a starter embodying the quick restarter and the lock-out meansand showing only the basic features of the starter and omitting thewiring connections.

In the schematic showing of the starters A in Figs. 6, 7 and 8, Adesignates an insulated base carrying contact pins 1, 2, 3, 4, and aninsulated upright A", which in practice are enclosed in a housing orcasing, not shown. On this upright are mounted a relay coil C, a springretracted relay armature switch S1, two thermally responsive orthermostatic switches S2, S3 and heaters H1 and H2 for the switches,which are connected in the manner shown in the disclosed circuitsemploying the switch S3 and its heater H2 for a lock-out action, whichswitch and its'heater may be omitted from a starter designed for generaluse but used most commonly in circuits not employing a lock-out action,the inclusion or omission of such switch and its heater-involving merelychanges in the wiring arrangements.

The switches, which are of self-closing type and normally closed are notphysically coupled for conjoint action, but are independently movable,switch S1 under action of the coil C and switches S2, S3, in response totheir heaters, with the exception that a quick restarter in the form ofa mechanical interlocking connection (controlled by the armatureactuated by the coil and generally designated MIC in Figs. 1 to 5) isinterposed between switches 51' and S2, and is provided for holdingswitch S2 open together with switch S1 under the electromagneticattraction of the coil C when the latter is energized. Coil C whenenergized acts only to pull switch S1 open after switch S2 has beenthermally opened, and in such action moves the interlocking connectioninto position to hold switch S2 in its open position.

This connection comprises an insulated arm A4 carried by the armatureswitch S1 which is free from connection with and normally allows fullopening movement of switch S2, but which moves into engagement at itsfree end with switch S2 when switch S1 is opened to hold switch S2 open,this holding action being due to the magnetic attraction of the coil. Acondenser C omitted in Figs. 6, 7 and 8, but shown in the disclosedcircuits, is included in the starter to reduce the arcing at thecontacts in accordance with customary practice. A stop A5 is provided tolimit the travel of thermal switch S3 when heated.

In the drawings I have shown various types of circuits for fluorescentlamps in which the starter A, in the forms disclosed, or by simplechanges in the wiring arrangements of parts, may be used to secureprompt and reliable starting and rapid restarting actions of a lamp ingood order and which may be used to secure a lockout action to avoidundue repetitive starting attempts if the lamp is defective or hasreached the end of its useful life period.

Referring to Fig. 1, showing a circuit for operation of D. Clamps, 5designates the lamp having a filamentary electrode 6 and a cooperatingelectrode 7, and 8b and 9b designate the input and output line leads orconductors extending from the positive and negative line terminals tothe starter terminals 1 and 3. The input and output portions of thecircuit include an inductive reactor R and ballast lamp BL located inthe conductor 8b ahead of the terminal 1, a conductor 10b leading fromthe starter terminal 2 to the input end of the filament 6, a conductor11b leading from the output end of the filament 6 to the starterterminal 4, and a conductor 8b at a point between the ballast lamp BLand starter terminal 1 to the electrode 7 which'is shown as beingshortcircuited.

Between the terminals 1 and 2 of the starter are serially arranged aportion or input part of the starter switch circuits which includes theconductors 12b, 13b, a magnetically operated switch S1, and athermostatic or thermally responsive cut-out switch S3. Extending acrossthis part of the starter circuit between conductors 12b, 13b is a heaterH2 for the switch and an arc suppressing condenser C. Heater H1 may bean open coil heater of 5-10 ohms resistance, while heater H2 ispreferably 0 I a carbon rod resistor of approximately 30,00050,000 ohms.With the arrangement described the switch S3 and its heater H2 areconnected across the lamp electrodes so as to be responsive undercertain conditions to unduly prolonged application of abnormal voltagesacrossthe electrodes when the lamp, after a number of attempts, refusesto fire, to cause said switch S3 to open and stop the operation of thestarter.

Another portion or output part of the starter switch circuits includesthe conductors 15b, 15b, the thermostatic switch S2, and a magnetic coilor winding C which controls the magnetic switch S1. Switch S2 isnormally closed and, when closed, connects the conductors 15b, 15b inseries with th e conductors 11b and 9b to complete the output portion pfthe preheating circuit, during 2 which it shunts the coil out of thiscircuit and renders the coil inactive. The parts just described asforming the output portion of the Starter preheating circuit areconnected in series with the input portion of the starter preheatingcircuit when all the switches are closed, ready for preheating thefilament when the line circuit is closed. Conductors 8b, 8b, the lampelectrodes, the gas of the lamp, conductor 11 b, coil C and conductor 9bform the component parts of the lamp operating circuit of the lamp.

In starting, preheating current flows from the positive side of theline,- through the reactor, through the ballast lamp to terminal 1 ofthe starter, through thermal switch S3, through heater H1, throughswitch S1, to terminal 2 of the starter, to and through the negativefilament 6 of the fluorescent lamp, thence to terminal 4 of the starter,through thermal switch S2 to terminal 3 of the starter, and thence tothe negative side of the line. During this time thermal switch S2 keepscoil C short circuited, and heater H2 is effectively short circuited dueto its being much higher in resistance than heater H1.

It will be noted in this circuit the ballast lamp is in the circuitduring preheating and regulates the preheating current, as well as theoperating current after the lamp has fired.

Preheating current continues to flow until heater H1 heats upsufficiently to cause the thermal switch S2 to open its contacts. Thiscuts coil C into the circuit, which opens switch S1 by magnetic action,thus breaking the preheating circuit rapidly, and causing the lamp if itis a good one to fire.

After the lamp fires, operating current flows from the positive side ofthe line, through the reactor and ballast lamp to the positive filament7 of the fluorescent lamp, through the gas in the lamp itself to thenegative filament 6, thence to terminal 4 of the starter, through relaycoil C to terminal 3 of the starter, and thence to the negative side ofthe line. The current flowing through coil C holds switch S1 open bymagnetic action and thermal switch S2 is held open by the mechanicalinterlock MIC.

During normal operation, heater H2 is connected across the fluorescentlamp itself, but the voltage drop across the lamp is not suflicient tocause it to heat up sufiiciently to cause thermal element S3 to open itscontacts.

If the line circuit is opened, switches S1 and S2 reclose immediately,so that the starter is ready for another starting action as soon as theline circuit is reclosed.

Should the lamp not fire on the first attempt however, it will makeseveral other attempts to fire, and each time that it does, the voltageapplied across heater H2 will be greater with switch S1 open while thelamp has not fired than if it had fired, this voltage beingsubstantially line voltage, instead of lamp voltage. After a number ofattempts to start, heater H2 will be heated sufficiently to cause thethermal switch S3 to open its contacts. This interrupts the circuit tothe lamp, except for the very small amount of current flowing throughheater H2, which will be substantially equal to line voltage beingapplied across heater H2, and which will be ample to hold switch S3 inits open position and cut out the starter although switches S1 and S2will reclose.

Under this condition, an appreciable time delay will be required(several minutes), when the circuit is opened for heater H2 to cool oflsuflicie'ntly to allow the contacts of thermal switch S3 to reclose, sothat the starter is ready to restart the lamp.

However, this delay can be avoided by replacing the defectivefluorescent lamp andthe starter at the same time. The starter can thenbe used in some other circuit later, as it will not have been damaged inany way.

The circuit shown in Fig. 2 is generally similar to that of Fig. 1except that conductor 80' leading to the cpeii-eircnited electrode 7 isdirectly connected with conductor 140, that a current limitingresistance R1 is provided in conductor 1%, and that a conductor 17,connecting conductor 8c with starter terminal 1, is connected directlyto the reactor ahead of the ballast lamp.

Thus while this circuit employs a multiple action lockout feature, theballast lamp is not in the circuit during preheating, which allows thepreheating current to: be adjusted separately by resistor R1. Also inorder to get the heater H2 across the lamp voltage after the lamp hasfired, it is necessary to use a special terminal, as indicated at 4'.

In this circuit when starting, preheating current flows from thepositive side of the line through the reactor, to terminal 1 of thestarter, through thermal switch S3, through heater Hi, through switchS1, to terminal 2 of the starter, through the resistor R1, through thenegative filament 6 of the fluorescent lamp, to terminal 4 of thestarter through thermal switch S2, to terminal 3 of the starter, andthence to the negative side of the line. A connection is also made fromthe low side of the ballast lamp to terminal 4 of the starter andthroughconductor tie to the positive filament. 7 of the fluorescentlamp, which in this case is not short-circuited. In the above describedstarting action, heater H2 is eflectively short-circuited by switch S1,heater H1 and the switch S3.

Preheating current continues to flow' until heater H1 heats thermalswitch S2 sufiiciently to cause it to open its contacts. When thisoccurs, coil C is energized by preheating current flowing throughnegative filament 6 of the lamp, causing it to open switch S1 and breakthe preheating circuit rapidly, thus firing the lamp, if in normalcondition. After the lamp has fired, coil C is kept energized by currentflowing through the lamp.

The operating circuit is from the positive side of the line, through thereactor, through the ballast lamp, to the positive filament 7 of thefluorescent lamp, through the gas in the lamp to the negative filament6, thence to terminal 4 of the starter, through coil C to terminal 3 ofthe starter, and thence to the negative side of the line.

Heater H2 being connected between terminals 2 and i of the starter, hasonly the voltage drop across the fluorescent lamp itself applied to it,and as in the case of Fig. 4 this voltage does not heat heater H2 enoughto cause thermal switch S3 to open its contacts.

This modified form of starter cannot be changed in its position in thesocket due to the special 5-contact base, so that there is no danger ofinterchanging any of the above connections.

If the line circuit is opened, switches S1 and S2 immediately recloseand the starter is ready for another starting action.

If, however, the lamp does not fire on the first attempt, it will makeseveral other attempts, and each time that switch S1 opens and the lampdoes: not fire, substantially line voltage will be applied to heater H2,so that it will heat up and cause thermal switch S3 to open. When switchS3 opens, current is removed from the lamp, except for the small amountof current that flows through heater H2 which is of high resistance.Switches S1 and S2 reclose, but as long as the line circuit is closedheater H2 holds switch S3 open.

With this condition, an appreciable time delay will be required (severalminutes) when the line circuit is opened for heater H2 to cool oifsuflicie'ntly to allow thermal switch S3 to reclose its contacts.

This time delay can be avoided, however, by replacing the defectivefluorescent lamp and the starter at the same time. The starter can thenbe used in some other circuit later, as it will not have been damaged inany way.

Lamps used in D. C. circuits having two filamentary electrodes, only oneof which is preheated to start the lamp, may have the positive filamentof the lamp short annexes circuited as in Fig. 4, or open-circuited asin Fig. 5, depending on the type of lamp and other characteristics ofthe circuit.

The circuit shown in Fig. 3 varies from'those shown in Figs. 1 and 2, inthat one line conductor'sd is connected by a conductor 82 with oneterminal of electrode 7, the other terminal of which is connected by aconductor d with starter terminal 2, while a conductor 10:: containing acurrent limiting resistance R1, connects the starter terminal 1 with theinput terminal of electrode 6, the arrangement of the switches S1, S2and S3 and coacting parts of the starter being otherwise the same asthat shown in Fig. 1.

This circuit is suitable for operating fluorescent lamps on either A. C.or D. C. When used on D. C., it has the disadvantage of having theballast lamp in the circuit during starting. When used on A. C., theballast lamp and resistor R1 can be omitted if the other re quirementsof the circuit permit it.

In this circuit when starting, preheating current flows from one side ofthe line through the reactor, through th ballast lamp (if used), throughfilament 7 of the fluorescent lamp to terminal 2 of the starter, thencethrough switch S1, heater H1 and thermal switch S3 to terminal 1 of thestarter, and through resistance R1 and filament 6 of the fluorescentlamp to'terminal 4 of the starter, through thermal switch S2 to terminal3 of the starter, and thence to the other side of the line. In thisconnection it should be borne in mind that on A. C. circuits, resistanceR1 might be zero and there might not be a ballast lamp, but the circuitpath would be the same.

As in the preceding circuits, preheating current continues to flow untilheater H1 heats up sufficiently to cause thermal switch S2 to open itscontacts, which cuts coil C into the preheating circuit and causesswitch S1 to open magnetically, thus breaking the preheating circuitrapidly and causing the lamp to fire if it is in good condition. Whilethe lamp is operating (or running) normally, coil C is kept energized bycurrent flowing through the lamp and holds switch S1 open by magneticaction and thermal switch S2 open by means of the mechanical interlockMIC.

While the lamp is operating normally, heater H2 is connected across thelamp voltage, which is not enough to heat it sufiiciently to cause thethermal switch S3 to open.

The operating circuit is from one side of the line, through the reactor,through the ballast lamp (if used), to filament 7 of the fluorescentlamp, through the gas of the lamp itself to the other filament 6, thenceto terminal 4 of the starter, through coil C to terminal 3 of thestarter and back to the other side of the line. If while the lamp isoperating normally, the line circuit is opened, switches S1 and S2 willreclose immediately, ready for another starting action. V

If the lamp does not start, however, the starter will make successiveattempts to start it, and each time switch S1 opens and the lamp doesnot fire, essentially line voltage is applied across heater H2. Therepeated application of this higher voltage causes. heater H2 to heat upsufficiently to cause thermal switch S3 to open, which cuts off allcurrent to the lamp except the small amount passing through heater H2which is of high resistance. Switches S1 and S2 reclose under thiscondition.

As in the other circuits employing the multiple action lockout featureand appreciable time delay (several minutes) will be required for heaterH2 to cool ofi sufficiently to allow thermal switch S3 to recloseafter'the line circuit is opened. However, this time delay can beavoided by replacing the defective fluorescent lamp and the starter atthe same time. The starter can then be used in some other circuit, as itwill not have been damaged in any way.'

Fig. 4 shows an operating circuit for short A. C. lamps and having themultiple lock-out feature and which is substantially the same as thecircuit shown in Fig. 3 with the exception of the omission of allfeatures pertaining to D. C. operation. The operation is the same asthat of circuit of Fig. 3 and hence need not be described in detail.

An advantage of this circuit is that it can be used satisfactorily forrelatively short A. C. fluorescent lamps that do not have suificientvoltage applied to them (particular ly when they have not fired) tocause current flow at low values after thermal switch S3 has opened itscontacts. With the connections shown, line voltage is still appliedacross the fluorescent lamp itself, even after thermal switch S3 hasopened its contacts.

Fig. 5 shows an operating circuit for A. C. fluorescent lamps using astarter with the lockout construction in which the parts are so arrangedthat the preheating or starting current and the operating current may beseparately adjusted. Thisis desirable in the case of lamps that are tofire and operate at low temperatures (0 F. and below). The starter hereshown is generally similar to that shown in Figs. 1, 3 and 4, with acertain change in construction, and with certain changes in the circuit.As shown, the switches S1, S2 and conducting connections 13b, 12b, 15b,15b, and 14b are similarly arranged to correspondingly functioning partsshown in Figs. 1 and 3, but there are changes and additions in thecircuit connections.

Conductors 9b and 11b are here arranged as in Figs. 1, 2, 3 and 4, but aconductor 8m extends from line terminal B to one terminal of electrode7, having its opposite terminal connected to starter terminal 2, while aconductor 10f connects starter terminal 1 with the input terminal ofelectrode 6. Resistance R1 is used in this circuit to control thepreheating current, and the ballast lamp BL and a resistance R2 areprovided in a connection across the starter terminals 3, 4 to controlthe operating current. A resistance R3 is also added in series with thecoil C in order to have it operate properly across the increased voltagedrop of resistance R2 and the ballast lamp after the lamp is startedinto operation.

In this circuit when starting, preheating current flows from terminal Bof the line through the reactor, through filament 7 of the fluorescentlamp to terminal 2 of the starter, through switch S1, through heater H1,through switch S3, to terminal 1 of the starter, through resistance R1,through the filament 6 of the fluorescent lamp to terminal 4 of thestarter, through the contacts of thermal switch S2 to terminal 3 of thestarter and thence back to the other line terminal line W. During thestarting action, thermal switch S2 contacts short-circuit the relaycoilC and resistance R3, as well as the ballast lamp and resistance R2.

The flow of preheating current continues until heater H1 has heatedthermal switch S2 sufliciently to cause it to open its contacts. Whenthis occurs, coil C is cut into the preheating circuit, which openscontacts S1 by magnetic action, breaking the preheating currentrapidlyand causing the lamp if in good condition to fire.

After the lamp has fired, operating current flows from one side B of theline through the reactor, to filament7 of the fluorescent lamp, throughthe gas in the lamp itself to the other filament 6, thence to terminal 4of the starter, where it divides, part flowing through coil C andresistance R3 to terminal 3 of the starter, and the other part throughthe ballast lamp and resistance R2 connected across the same terminalsof the starter, thence to the other side W of the line. Ballast lamp BLand resistance R2 can be selected to provide the proper operating(running current) thus permitting the reactor to be made of lessreactance than would usually be the case, in order to allow more currentto flow during preheating and make starting of the fluorescent lampeasier at low temperatures, such as 0 F. and below.

As in the other circuits previouslydescribed, if the line circuit isopened while the lamp is operating normally, coil C of the relay istie-energized, allowing switches S1 and S2 to reclose immediately readyfor another starting action.

During a normal starting action, heater H2 is efiectivelyshort-circuited and takes no part in it. After the lamp has fired,-heater H2 is connected across lamp voltage but this does not produceenough heat in it to cause thermal switch S3 to open its contacts.

It the lampdoes not fire on the first attempt, however, the starter willmake a number of other attempts to do so. Each time that switch S1 isopened with the lamp not having fired, essentially line voltage isimpressed across the heater H2, finally heating it sufiiciently to causethermal switch S3 to open its contacts.

In the open position of thermal switch S3, heater H2 is practicallyacross line voltage and this opens the circuit through the lamp,- exceptfor" the small amount of current passing through heater H2. Switches S1and S2 reclose under this condition. Line voltage is applied across thelam terminals in the cut-out position.

As in the case of the other circuits previously described having themultiple action lockout feature, an appreciable time delay will beinvolved after the line circuit is opened for heater H2 to cool oilsufficiently to allow thermal switch S3 to reclose its contacts.

This time delay can be avoided by replacing the defective fluorescentlamp and the starter at the same time as has been previously described.

This circuit of Fig.- 5, as stated, has the desirable feature that thestarting current may be adjusted to a higher value than normal in orderto effect starting at low temperatures, and that the reactor R may be ofa lower reactance than that which would normally be used in the circuitwhen operated at room temperatures in order to secure this higherstarting current.

The heater H2 for thermal switch S3 is shown in Figs. 1 and 4 as beingconnected directly across the lamp electrodes 6 and 7, while in Figs. 2,3 and 5 heater H3 is connected across the electrodes 6 and 7 and theresistance R1 in series therewith. However, since the value ofresistance R1 is low its presence does not affect to any appreciableextent the voltage impressed across heater H3, and it will be understoodthat the expression across the electrodes, as used in the appendedclaims, includes either of these circuit arrangements.

A starter embodying the present invention has the following two majoradvantages over prior starters, to wit, (1) The preheating orstartingcircuit is broken rapidly by the opening of switch Si by magnetic means.This causes the reactor to give a higher inductive kick than thatobtained from the slower opening of straight thermal or glow switchstarters when used in the same circuits. The higher inductive kick notonly makes the firing more certain, but will also effect the firing oflamps that might be discarded under the impression that they had reachedthe end of their useful life period. (2) In all normal operation oflamps, due to the switch S1 being held open magnetically by the coil Cby the flow of current through the lamp, the switch will openimmediately if the line circuit is opened, and in so doing allow switchS2 to also reclose, so that the starter is ready for anotherstarting'action as soon as the line circuit is reclosed. This is not soin the case of a straight thermal starter, where it is necessary for theheater to cool cit before its contacts can reclose.

This ability of obtaining a quick resetting action of the parts toobtain an immediate restart applies,- of course, to the starters usedwith the lock-out feature and when the starter is used with a good lamp.In the case of the use of a starter having the lock-out feature,however, the thermal units used for the lock-out action if they comeinto action take an appreciable length of time (several minutes) to cooloff before restarting action can again take place. However, this delaycan be avoided, as pre- 8 viously pointedout,- when applying a new lampin place of the defective lamp, by removing the staiter which has beenin use and applying a new starter, in which case the starter removed maybe used as soon as it cools off in some other circuit.

From the foregoing description, taken in connection with the drawings,the construction and operation of the starter and various circuitsdisclosed will be readily understood without a further and extendeddescription, and it will be seen that the invention provides a starterof simple and economical type which facilitates and renders easier thestarting of hard starting lamps, and one which, if desired, providesmeans for locking out the starter from continuous or undesired repeatingactions to prevent damage to the starter or other components of thecircuit inthe case of a defective lamp, or a lamp which has reached theend of its useful life. While the constructions shown for these purposesare preferred, it is to be understood that they are merelyexemplificative, and that changes in the form, construction and arrangement of parts, falling within the scope of the appended claims, may bemade Without departing from the spirit of the invention;

Having thus described my invention 1 claim:

1. In a system for starting and operating electric discharge devicescomprising a gaseous electric discharge device of the low pressure typehaving two electrodes at least one of which is constructed to receivepreheating current, a supply circuit, a normally closed thermallyresponsive shunting switch having an operating heater, a normally closedelectromagnetic starting switch having an operating winding, meansincluding an inductive reactance device and the winding of said startingswitch for connecting said electrodes to said supply circuit, apreheating circuit capable of producing firing temperature electrodeheating, said circuit extending from one side of a voltage source to theopposite side of said source and including in series connection saidinductive reactance device and the heater for said shunting switch andat least one of said electrodes and said starting and shunting switches,said shunting switch being connected in shunt with the winding of saidstarting switch so that the opening of said shunting switch causes theenergization of said winding and the consequent opening of said startingswitch thereby causing the discharge device to fire by an inductivevoltage kick, said starting switch being connected in shunt with saidelectrodes, and mechanical means o'peratively interconnecting saidstarting and shunting switches to hold the shunting switch open afterthe heater therefor cools, the operating current of said dischargedevice continuing to energize said winding and hold both of saidswitches open during the operation of the discharge device, thecombination with said system of a normally closed thermally responsivecut-out switch included in the said preheating circuit, and a heatertherefor connected at all times across the electrodes of the dischargedevice.

2. In a system for starting and operating electric discharge devices asset forth in claim 1 in which the heater for the cut-out switch isconnected across the electrodes of the discharge device and in parallelwith a circuit including in series connection the starting and cut-outswitches and the heater for the shunting switch so that when thec'ut-out switch opens the heater therefor is connected in series withthe starting switch winding, the

said heater not allowing sufiicient current to flow to operate thestartingswitc'h.

3. In a system'tor starting and operating electric discharge devicescomprising a gaseous electric discharge device of the low pressure typehaving two electrodes constructed to receive preheating current, asupply circuit, a normally closed thermally responsive shunting switchhaving an operating heater; a normally closed electromagnetic startingswitch having an operating winding, means including an inductivereactan'ce device and the "new.

winding of said starting switch for connecting said electrodes to saidsupply circuit, a preheating circuit capable of producing firingtemperature electrode heating, said circuit extending from one side of avoltage source to the opposite side of said source and including inseries connection said inductive reactance device and the heater forsaid shunting switch and said electrodes and said starting and shuntingswitches, said shunting switch being connected in shunt with the windingof said starting switch so that the opening of said shunting switchcauses energization of said winding and the consequent opening of saidstarting switch thereby causing the discharge device to fire by aninductive voltage kick, said starting switch being connected in shuntwith said electrodes, and mechanical means operatively connecting saidstarting and shunting switches to hold the shunting switch open afterthe heater therefor cools, the operating current of said dischargedevice continuing to energize said winding and hold both of saidswitches open during the operation of said discharge device, thecombination with said system of a normally closed thermally responsivecut-out switch and a heater therefor, said cut-out switch beingconnected in that portion of the preheating circuit extending from oneelectrode through the heater for said shunting switch and thence throughthe starting switch to the opposite electrode, and said cut-out switchheater being connected at all times across said electrodes.

4. A system for starting and operating electric discharge devices as setforth in claim 3 in which the shunting switch is connected in shunt witha circuit including the winding of the starting switch and a currentlimiting resistance arranged in series connection, and a circuit isconnected in shunt with said circuit which comprises a ballast lampconnected in series with a current controlling resistance.

References Cited in the file of this patent UNITED STATES PATENTS2,339,051 Cates Jan. 11, 1944 2,341,520 Babb Feb. 15, 1944 2,438,557Hehenkamp Mar. 30, 1948

